Recently, with the development of information communications and the increasing demands for multimedia services, a base station technique that provides a service in a combined form of an existing network at home or indoors is required. To this end, a femtocell concept has been introduced in order to provide a data service at a high speed while solving defects occurring when providing a service at an indoor radio wave shadow area. The standardization and technical development thereof are in progress. The standardization of a femtocell started from 3GPP and 3GPP2 in 2007. Several issues such as a femtocell network structure, an interface scheme, a handover procedure, selection of an access system, mobility management and synchronization and the like have been discussed.
The foregoing femtocell satisfies requirements in a user service and has an effect of saving installation and maintenance time and operating costs of a base station, by allowing an installation and a change of a cell providing a service to be within a space like home or an office. Further, such a femtocell can increase a frequency usage rate by minimizing a cell size, and provide an existing wired wideband service at low costs even in a mobile communications network. In addition, when a femtocell is introduced to an indoor environment to provide a service, since a conventional mobile terminal that accesses a wideband wireless access service in the indoor environment by employing a cellular and WLAN dual mode function can provide a service by using only a cellular mode, it has a merit in that the cost thereof is lowered.
Further, the femtocell has a very small cell region in comparison to the macro cell, and thus, multiple femtocells may be installed in a single macro cell region. Also, the femtocell may be installed by mobile communication carriers in a service shadow area and an area with a high population density such as a shopping mall such that the service can be provided to registered subscribers, or installed directly by a subscriber in a limited space such as a home such that the subscriber can receive the service.
In this femtocell, since a service region is very small and an installation thereof is easy, multiple femtocells may be provided in a single macro cell. Thus, managing the femtocell by a cell planning like an existing macro cell is very difficult. Also, the femtocell may provide a service by using the same frequency as that of a macro cell and a neighbor femtocell. Therefore, since there is interference between cells, a frequency configuration scheme of a femto access point (FAP) that takes into consideration interference is required.
That is, in an environment where macro cells and femtocells are mixed, when a mobile terminal is connected to a macro cell and a channel environment is good, the mobile terminal does not search and access a femtocell although the femtocell is present in an adjacent position. In this case, communication between the mobile terminal and the macro cell acts as serious interference to the femtocell.
Further, a mobile terminal requires functions of estimating and searching a position of a femtocell and determining whether or not to access thereto, in order to receive a service provided by the femtocell. In case where a mobile terminal can support a global positioning system (GPS) function and receive a GPS signal, position information measured by the mobile terminal and position information on an FAP may be compared to search the femtocell. However, in case where a mobile terminal with no GPS function or a mobile terminal with a GPS function enters indoor to which a GPS signal cannot be received, it fails to obtain position information on the mobile terminal.
In this case, the mobile terminal does not recognize the femtocell and accesses a macro cell to receive a service or periodically performs a scanning procedure for searching a femtocell. Thus, battery consumption of the mobile terminal is great and a search time increases.